- Email: [email protected]
Response of the endolymphatic sac in the guinea pig to neomycin ototoxicity
Am ] Otolaryngnl 3:254-281, 1982
Response of the Endolymphatic Sac in the Guinea Pig to Neomycin Ototoxicity ROGERF. GRAY,F.R.C.S.,* ROBERTA. SCHINDLER,M.D., KATYY. CHEN,M.S,, ZHI-ZHONGWANG, M.D.,'I" ANDFRANKWILSON,F.R.C.S.$ The guinea pig provides an excellent model for studying the effects of ototoxic antibiotics on the epithelium of the endolymphatic sac (ELS). Intracochlear injection of neomycin produces consistent destruction of cochlear and vestibular sensory cells, and the response to this traumatic insult can be documented by light and electron microscopy of the ELS. The histolegic findings suggest that ELS epithelial cells are relatively resistant to ototoxic levels of neomycin. The study confirms the ability of the ELS to increase its activity during periods of labyrinthine stress. (Key words: Aminogiycoside antibiotics; Endolymphatic sac; Neomycin; Ototoxicity.)
METHODS AND MATERIALS
The epithelium of the e n d o l y m p h a t i c sac (ELS) is embryologically derived from stem cells of the otocyst. Except for their location within the otocyst, these stem cells might differentiate into vestibular or cochlear hair cells. It is well known that ototoxic drugs, specifically aminoglycoside antibiotics, have a peculiarly destructive effect on the sensory hair cells. I-3 It is less clear whether these ototoxic agents will damage or destroy other derivatives of the otocyst, specifically the epithelium of the ELS. The goal of this study has been to answer this question. This report describes the pathologic changes in the ELS in response to the intracochlear injection of neomycin in the guinea pig. This a n i m a l provides an excellent e x p e r i m e n t a l model because the histologic features of its normal and activated ELS have been described in detail.4-6 From the (1) S. & I. Epstein Otoneurological Laboratory, Department of Otolaryngology,Universityof California,San Francisco, California. Received December 29, 1981. Accepted for publication February 23, 1982. Supported by the S. &I. Epstein EndowmentFund. * Present address: The Royal Free Hospital, London, England. ~"Present address: The CapitalHospital, ChineseAcademy of Sciences, Beijing,Peoples Republic of China. * Present address: University Hospital of Wales, Cardiff, Wales. Address correspondence and reprint requests to Dr. Schindler: Department of Otolaryngology,S. & I. Epstein LaboratoryHSE 863, Universityof California,San Francisco, California 94143. 0196-07091821070010254
Thirty-five young guinea pigs weighing between 230 and 300 g were used in this study, Each animal was subjected to intracochlear injection via the round window of 20/zl of a 20 per cent solution of n e o m y c i n sulfate (4,000 ttg). Anesthesia was achieved with a combination of Innovar-Vet (droperidol and fentanyl) and ketamine. The round w i n d o w was exposed by opening the bulla through a postauricular incision. A Unimetrics syringe with a drawn glass micropipette was attached to a micromanipulator. The tip of the micropipette was driven through the round w i n d o w membrane under microscopic control and the n e o m y c i n solution was instilled into the scala tympani in 4 to 6 minutes. Animals were accepted for the study if they d e m o n s t r a t e d a vestibular response that included a circular gait toward the injected ear and appropriate nystagmus. The guinea pigs were sacrificed while anesthetized with methoxyflurane and oxygen one day, two days, three days, seven days, and six weeks after the injection of neomycin. The temporal bones were removed from decapitated animals and perfused with cold 0.1 M phosphate-buffered 2 percent g l u t a r a l d e h y d e a n d 2 per cent p a r a f o r m a l dehyde. Sac specimens were fixed in 1 per cent osmium tetroxide, dehydrated, dissected, and embedded in Epon. Sections 1 /zm thick were
$01.6e 9 W. B. Sounders Co. 254
GRAYET AL. cut on the LKB ultratome and stained with toluidine blue for light microscopic study. Ultrathin sections were prepared, stained with uranyl acetate and lead citrate, and examined with a JEOL 100S electron microscope. RESULTS
Cochlear and Vestibular Hair Cells All of the hair cells in the cochlea showed evidence of acute toxicity and degeneration (Fig. 1, A and B). Large vacuoles were present in the cytoplasms of the inner and outer hair cells. Cellular debris could be seen in the perilymphatic and endolymphatic fluid spaces. Supporting elements along the basilar partition were also damaged. After seven days cells of the organ of Corti were no longer identifiable and had been replaced by a single layer of low cuboidal epithelium along the basilar membrane and spiral lamina. The stria vascularis appeared thinner than normal, but the surface epithelial cells on it and Reissner's membrane remained intact. The vestibular apparatus showed similar evidence of hair cell degeneration, with vacuolation, swelling and separation of hair cells in the one- and three-day survivors (Fig. 1C). By seven days all that remained of the cristae and maculae were mounds that were devoid of hair cells and resurfaced with cuboidal epithelial cells.
Normal Sac The ELS of the guinea pig has three more or less distinct parts: a dilated terminal area (pars distalis), a rugose portion (pars intermedius), and a portion within bony walls that tapers to join the endolymphatic duct (pars proximalis). The endolymphatic sac is lined with a single layer of large (7 to 10 ~m in diameter) basaphilic cells whose nuclei and cytoplasm vary in electron density. The cell bases are attached to a basement membrane and the cell apices are tightly bound in tripartite junctions to one another. The l u m e n of the ELS contains a basophilic fluid that contains free-floating cells and cellular debris. The most active region of the ELS is the pars intermedius or rugose part, where the surface epithelium is convoluted into true villous projections.
One Day after Injection of Neomycin
showed variations of electron density, with some specimens demonstrating dark, concentrated intraluminal fluid while others evidenced pale, dilute endolymph (Fig. 2A). The epithelial cells were relatively compact, with few dilated intracellular fluid spaces (Figs. 3, A and B). Occasional heterophagic vesicles were present in the cytoplasm, and a few macrophages could be seen in the ELS lumen. Both these features were also found in the untreated control ELS.
Two to Three Days after Injection of Neomycin Many of the features of the normal ELS epithelium were still retained; but, in contradistinction to one-day survivors, many cells had increased numbers of small vacuoles and darklystained, membrane-bound inclusions. Many of these inclusions were grouped around a prominent Golgi apparatus, while others were clustered near the cell periphery. The epithelium remained intact as a single layer of ceils, but these cells appeared more loosely attached or bound to one another and to the basement membrane. Nowhere was epithelial ulceration evident (Fig. 2B). The intercellular fluid spaces were enlarged, and the contrast between the electron-dense endolymph and the clear intercellular space was marked. Active phagocytosis of endolymphatic debris could be seen at the luminal surface, and many more fragments o f disintegrating neuroepithelial cells were evident in the ELS lumen (Fig. 4, A and B).
Seven Days after Injection of Neomycin After seven days many of the multivesicular bodies and heterophagic vesicles persisted in the cytoplasm. However, many of these membranebound, dark bodies were evident at the base and sides of the cell rather than in the surface cytoplasm. Large free-floating, intraluminal macrophages packed with debris remained, as did some cellular detritus. In addition, the number of macrophages in the subepithelial connective tissue had increased. The fluid in the ELS was still electron-dense, and the epithelial cells appeared more firmly attached to the basement membrane, with smaller but still dilated intercellular spaces (Fig. 2C).
Six Weeks after Injection of Neomycin Epithelial cells of the ELS appeared largely unaffected by the cochlear and vestibular insult. As in normal controls, the endolymph in the ELS
The ELS lumen was relatively clear of cells. As in the normal controls, the endolymph varied
Volume 3 Number 4 July 1982
255
NEOMYCIN
TOXICITY
IN ENDOLYMPHATIC
SAC
A /
D
C
2 '~
A,rneric(~ n
Journal of
Otolaryng01ogy 256
~
"~
i,, ~:~
Figure 1. Light photomicrographs of A., cross section of the cochlea of a guinea pig three days after injecti.on of neomycin. Notice the degenerating organ of Corti (arrow}; B, detail of the apical turn of the organ of Corti of a guinea pig three days after injection of neomycin. The hair cell degeneration is complete. C, the erista ampullaris one day after injection of neomycin. Notice the degenerating vestibular hair cells (arrow}. Toluidlne blue.
GRAY ET AL.
Figure 2. Light photomicrographs of the endolymphatic sac (ELS) of guinea pigs, A, one day after injection of neomycin, the lumen of the ELS has relatively few flee-floating cells. B, two days after injection of neomycin, Notice the darkly stained endolymph and numerous flee-floating cells. C, seven days after injection of neomycin. Numerous free-floating cells and debris remain. D, six weeks after injection of neomycin. Notice that the ELS ceils and lumen appear nearly normal. Toluidine blue.
Volume 3 Number 4 July 1982 257
NEOMYCIN TOXICITY IN ENDOLYMPHATIC SAC
American Journal of Otolaryn gol0gy 258
Figure 3, A, electron photomicrograph of a normal~appearing endolymphatic sac (ELS) one day after injection of neomycin. Notice the relatively clear end01ymph (L) and the prominent basement membrane (arrow) surrounding the ELS cells. B, ELS cells are closely grouped with typical tripartite iunctions (arrow) near the luminal surface [L). Uranyl acetate and lead citrate.
GRAY ET AL.
Figure 4. Electron photomicrograph of the endolymphatic sac (ELS) two days after the injection of neomycin, A, the ELS lumen (L) is filled with electron-dense endolymph and cellular detritus (arrow), B, large heterophagic vacuoles (arrow) are visible in the ELS cells, and the intercellular fluid spaces (ICS) are relatively clear compared with the electron.dense endolymph (L). Uranyl acetate and lead citrate,
Volume 3 Number 4 July 1982 259
NEOMYCIN TOXICITY IN ENDOLYMPHATIC SAC
Figure 5. Electron photomicrograph of the endolymphatic sac (ELS) six weeks after injection of neomycin. The ELS epithelial ceils appear nearly normal. Uranyl acetate and lead citrate.
from pale to dark. The epithelial cell layer was indistinguishable from that of the normal controls except for the p r e s e n c e of n u m e r o u s heterophagic vacuoles in the cytoplasm. The subepithelial connective tissue was largely unchanged from that of the controls and had only an occasional macrophage. Nowhere was there evidence of formation of scar tissue or deposition of collagen (Figs. 2D and 5). DISCUSSION AND CONCLUSIONS
A n'le rico n
Journal
of Otolaryngalogy 260
Intracochlear, p e r i l y m p h a t i c i n j e c t i o n of neomycin produced extensive destruction of the neuroepithelium of the cochlea and vestibular apparatus. Typically, cochlear hair cells and sustentacular elements were completely destroyed, leaving only a single layer of epithelial cells along the basilar membrane. The vestibular apparatus showed similar hair cell losses in the cristae and maculae. The epithelium of the ELS responded to this labyrinthine insult in much the same way as has been previously described for other experimentally induced inner ear trauma. 7 Of interest is that the ELS epithelium underwent changes re-
flecting increased cellular activity after direct perilymphatic iniection of neomycin that paralleled the extent of cellular destruction within the cochlea and vestibular apparatus. In neomycininjected animals ELS cells maintained an appearance of continuing function by concentrating endolymph and phagocytosing cellular detritus. This ELS response probably resulted from the destruction of other cellular elements in the labyrinth which released into the endolymph compounds that stimulated epithelial cells in the ELS to increase their activity. H o w this labyrinthine t r a u m a - E L S reaction was mediated remains unknown. Clearly, the reaction began within 48 hours and continued for several days to weeks after the insult. Interestingly, the increase in ELS activity in response to perilymphatic injection of neomycin was prolonged when compared with ELS responses to specific labyrinthine insults, such as freezing the lateral ampulla. The ELS responses seen in this study reinforce the observations of others that aminoglycoside antibiotics have an ongoing destructive effect on cellular elements in the guinea pig cochlea and vestibular apparatus for periods of at leas[ several weeks, s,:~
GRAY ET AL.
The present study confirms the finding that the ELS increases its activity during periods of labyrinthine trauma and stress. Further, the present study suggests that, like some other cellular elements derived from the otocyst, most notably the strial epithelium and Reissner's membrane, the epithelium of the endolymphatic sac is not d e s t r o y e d by ototoxic levels of aminoglycoside antibiotics.
4.
5.
6. 7.
References 8. 1. Kohonen A: Effect of some ototoxic drugs upon the pattern and innervation of cochlear sensory cells in the guinea pig. Acta Otolaryngol suppl 208:1-70, 1965 2. Hunter-Duvar IM, Mount RJ: The organ of Corti following ototoxic antibiotic treatment, SEM/1978/II, pp 423 - 4 2 9 3. Leake-Jones PA, Vivion MC: Cochlear pathology in cats
9.
following administration of neomycin sulphate. SEM/ 1979/III, pp 983-991 Lundquist P-G: The endalymphatic duct and sac in the guinea pig. An electron microscopic and experimental investigation. Acta Otolaryngol suppl 201:1-108, 1965 Lundquist P-G, Kimura R, Wers~lll J: Ultrastructural organization of the epithelial lining in the endolymphatic duct and sac in the guinea pig. Acta Otolaryngol 57:65-80, 1965 Lundquist P-G: Aspects on endolymphatic sac morphology and function. Arch Oto-Rhino-Laryngal 212:231 240, 1976 Schindler RA, Lundquist P-G, Morrison MD: Endolymphatic sac response to cryosurgery of the lateral ampulla. Ann Otol Rhinol Laryngol 83:674--685, 1974 T e r a y a m a Y, Kaneko Y, Kawamoto K, et al: Ultrastructural changes of the nerve elements following disruption of the organ of Corti. Acta Otolaryngol 83:291-302, 1977 Kaneko Y, Terayama Y, Kawamoto K, et ah Single layer membrane covering the degenerated cochlear duct after perilymphatic perfusion of streptomycin. Acta Otolaryngol 86:375-384, 1978
Volume 3 Number 4 July 1982 2 (~1
Response of the Endolymphatic Sac in the Guinea Pig to Neomycin Ototoxicity ROGERF. GRAY,F.R.C.S.,* ROBERTA. SCHINDLER,M.D., KATYY. CHEN,M.S,, ZHI-ZHONGWANG, M.D.,'I" ANDFRANKWILSON,F.R.C.S.$ The guinea pig provides an excellent model for studying the effects of ototoxic antibiotics on the epithelium of the endolymphatic sac (ELS). Intracochlear injection of neomycin produces consistent destruction of cochlear and vestibular sensory cells, and the response to this traumatic insult can be documented by light and electron microscopy of the ELS. The histolegic findings suggest that ELS epithelial cells are relatively resistant to ototoxic levels of neomycin. The study confirms the ability of the ELS to increase its activity during periods of labyrinthine stress. (Key words: Aminogiycoside antibiotics; Endolymphatic sac; Neomycin; Ototoxicity.)
METHODS AND MATERIALS
The epithelium of the e n d o l y m p h a t i c sac (ELS) is embryologically derived from stem cells of the otocyst. Except for their location within the otocyst, these stem cells might differentiate into vestibular or cochlear hair cells. It is well known that ototoxic drugs, specifically aminoglycoside antibiotics, have a peculiarly destructive effect on the sensory hair cells. I-3 It is less clear whether these ototoxic agents will damage or destroy other derivatives of the otocyst, specifically the epithelium of the ELS. The goal of this study has been to answer this question. This report describes the pathologic changes in the ELS in response to the intracochlear injection of neomycin in the guinea pig. This a n i m a l provides an excellent e x p e r i m e n t a l model because the histologic features of its normal and activated ELS have been described in detail.4-6 From the (1) S. & I. Epstein Otoneurological Laboratory, Department of Otolaryngology,Universityof California,San Francisco, California. Received December 29, 1981. Accepted for publication February 23, 1982. Supported by the S. &I. Epstein EndowmentFund. * Present address: The Royal Free Hospital, London, England. ~"Present address: The CapitalHospital, ChineseAcademy of Sciences, Beijing,Peoples Republic of China. * Present address: University Hospital of Wales, Cardiff, Wales. Address correspondence and reprint requests to Dr. Schindler: Department of Otolaryngology,S. & I. Epstein LaboratoryHSE 863, Universityof California,San Francisco, California 94143. 0196-07091821070010254
Thirty-five young guinea pigs weighing between 230 and 300 g were used in this study, Each animal was subjected to intracochlear injection via the round window of 20/zl of a 20 per cent solution of n e o m y c i n sulfate (4,000 ttg). Anesthesia was achieved with a combination of Innovar-Vet (droperidol and fentanyl) and ketamine. The round w i n d o w was exposed by opening the bulla through a postauricular incision. A Unimetrics syringe with a drawn glass micropipette was attached to a micromanipulator. The tip of the micropipette was driven through the round w i n d o w membrane under microscopic control and the n e o m y c i n solution was instilled into the scala tympani in 4 to 6 minutes. Animals were accepted for the study if they d e m o n s t r a t e d a vestibular response that included a circular gait toward the injected ear and appropriate nystagmus. The guinea pigs were sacrificed while anesthetized with methoxyflurane and oxygen one day, two days, three days, seven days, and six weeks after the injection of neomycin. The temporal bones were removed from decapitated animals and perfused with cold 0.1 M phosphate-buffered 2 percent g l u t a r a l d e h y d e a n d 2 per cent p a r a f o r m a l dehyde. Sac specimens were fixed in 1 per cent osmium tetroxide, dehydrated, dissected, and embedded in Epon. Sections 1 /zm thick were
$01.6e 9 W. B. Sounders Co. 254
GRAYET AL. cut on the LKB ultratome and stained with toluidine blue for light microscopic study. Ultrathin sections were prepared, stained with uranyl acetate and lead citrate, and examined with a JEOL 100S electron microscope. RESULTS
Cochlear and Vestibular Hair Cells All of the hair cells in the cochlea showed evidence of acute toxicity and degeneration (Fig. 1, A and B). Large vacuoles were present in the cytoplasms of the inner and outer hair cells. Cellular debris could be seen in the perilymphatic and endolymphatic fluid spaces. Supporting elements along the basilar partition were also damaged. After seven days cells of the organ of Corti were no longer identifiable and had been replaced by a single layer of low cuboidal epithelium along the basilar membrane and spiral lamina. The stria vascularis appeared thinner than normal, but the surface epithelial cells on it and Reissner's membrane remained intact. The vestibular apparatus showed similar evidence of hair cell degeneration, with vacuolation, swelling and separation of hair cells in the one- and three-day survivors (Fig. 1C). By seven days all that remained of the cristae and maculae were mounds that were devoid of hair cells and resurfaced with cuboidal epithelial cells.
Normal Sac The ELS of the guinea pig has three more or less distinct parts: a dilated terminal area (pars distalis), a rugose portion (pars intermedius), and a portion within bony walls that tapers to join the endolymphatic duct (pars proximalis). The endolymphatic sac is lined with a single layer of large (7 to 10 ~m in diameter) basaphilic cells whose nuclei and cytoplasm vary in electron density. The cell bases are attached to a basement membrane and the cell apices are tightly bound in tripartite junctions to one another. The l u m e n of the ELS contains a basophilic fluid that contains free-floating cells and cellular debris. The most active region of the ELS is the pars intermedius or rugose part, where the surface epithelium is convoluted into true villous projections.
One Day after Injection of Neomycin
showed variations of electron density, with some specimens demonstrating dark, concentrated intraluminal fluid while others evidenced pale, dilute endolymph (Fig. 2A). The epithelial cells were relatively compact, with few dilated intracellular fluid spaces (Figs. 3, A and B). Occasional heterophagic vesicles were present in the cytoplasm, and a few macrophages could be seen in the ELS lumen. Both these features were also found in the untreated control ELS.
Two to Three Days after Injection of Neomycin Many of the features of the normal ELS epithelium were still retained; but, in contradistinction to one-day survivors, many cells had increased numbers of small vacuoles and darklystained, membrane-bound inclusions. Many of these inclusions were grouped around a prominent Golgi apparatus, while others were clustered near the cell periphery. The epithelium remained intact as a single layer of ceils, but these cells appeared more loosely attached or bound to one another and to the basement membrane. Nowhere was epithelial ulceration evident (Fig. 2B). The intercellular fluid spaces were enlarged, and the contrast between the electron-dense endolymph and the clear intercellular space was marked. Active phagocytosis of endolymphatic debris could be seen at the luminal surface, and many more fragments o f disintegrating neuroepithelial cells were evident in the ELS lumen (Fig. 4, A and B).
Seven Days after Injection of Neomycin After seven days many of the multivesicular bodies and heterophagic vesicles persisted in the cytoplasm. However, many of these membranebound, dark bodies were evident at the base and sides of the cell rather than in the surface cytoplasm. Large free-floating, intraluminal macrophages packed with debris remained, as did some cellular detritus. In addition, the number of macrophages in the subepithelial connective tissue had increased. The fluid in the ELS was still electron-dense, and the epithelial cells appeared more firmly attached to the basement membrane, with smaller but still dilated intercellular spaces (Fig. 2C).
Six Weeks after Injection of Neomycin Epithelial cells of the ELS appeared largely unaffected by the cochlear and vestibular insult. As in normal controls, the endolymph in the ELS
The ELS lumen was relatively clear of cells. As in the normal controls, the endolymph varied
Volume 3 Number 4 July 1982
255
NEOMYCIN
TOXICITY
IN ENDOLYMPHATIC
SAC
A /
D
C
2 '~
A,rneric(~ n
Journal of
Otolaryng01ogy 256
~
"~
i,, ~:~
Figure 1. Light photomicrographs of A., cross section of the cochlea of a guinea pig three days after injecti.on of neomycin. Notice the degenerating organ of Corti (arrow}; B, detail of the apical turn of the organ of Corti of a guinea pig three days after injection of neomycin. The hair cell degeneration is complete. C, the erista ampullaris one day after injection of neomycin. Notice the degenerating vestibular hair cells (arrow}. Toluidlne blue.
GRAY ET AL.
Figure 2. Light photomicrographs of the endolymphatic sac (ELS) of guinea pigs, A, one day after injection of neomycin, the lumen of the ELS has relatively few flee-floating cells. B, two days after injection of neomycin, Notice the darkly stained endolymph and numerous flee-floating cells. C, seven days after injection of neomycin. Numerous free-floating cells and debris remain. D, six weeks after injection of neomycin. Notice that the ELS ceils and lumen appear nearly normal. Toluidine blue.
Volume 3 Number 4 July 1982 257
NEOMYCIN TOXICITY IN ENDOLYMPHATIC SAC
American Journal of Otolaryn gol0gy 258
Figure 3, A, electron photomicrograph of a normal~appearing endolymphatic sac (ELS) one day after injection of neomycin. Notice the relatively clear end01ymph (L) and the prominent basement membrane (arrow) surrounding the ELS cells. B, ELS cells are closely grouped with typical tripartite iunctions (arrow) near the luminal surface [L). Uranyl acetate and lead citrate.
GRAY ET AL.
Figure 4. Electron photomicrograph of the endolymphatic sac (ELS) two days after the injection of neomycin, A, the ELS lumen (L) is filled with electron-dense endolymph and cellular detritus (arrow), B, large heterophagic vacuoles (arrow) are visible in the ELS cells, and the intercellular fluid spaces (ICS) are relatively clear compared with the electron.dense endolymph (L). Uranyl acetate and lead citrate,
Volume 3 Number 4 July 1982 259
NEOMYCIN TOXICITY IN ENDOLYMPHATIC SAC
Figure 5. Electron photomicrograph of the endolymphatic sac (ELS) six weeks after injection of neomycin. The ELS epithelial ceils appear nearly normal. Uranyl acetate and lead citrate.
from pale to dark. The epithelial cell layer was indistinguishable from that of the normal controls except for the p r e s e n c e of n u m e r o u s heterophagic vacuoles in the cytoplasm. The subepithelial connective tissue was largely unchanged from that of the controls and had only an occasional macrophage. Nowhere was there evidence of formation of scar tissue or deposition of collagen (Figs. 2D and 5). DISCUSSION AND CONCLUSIONS
A n'le rico n
Journal
of Otolaryngalogy 260
Intracochlear, p e r i l y m p h a t i c i n j e c t i o n of neomycin produced extensive destruction of the neuroepithelium of the cochlea and vestibular apparatus. Typically, cochlear hair cells and sustentacular elements were completely destroyed, leaving only a single layer of epithelial cells along the basilar membrane. The vestibular apparatus showed similar hair cell losses in the cristae and maculae. The epithelium of the ELS responded to this labyrinthine insult in much the same way as has been previously described for other experimentally induced inner ear trauma. 7 Of interest is that the ELS epithelium underwent changes re-
flecting increased cellular activity after direct perilymphatic iniection of neomycin that paralleled the extent of cellular destruction within the cochlea and vestibular apparatus. In neomycininjected animals ELS cells maintained an appearance of continuing function by concentrating endolymph and phagocytosing cellular detritus. This ELS response probably resulted from the destruction of other cellular elements in the labyrinth which released into the endolymph compounds that stimulated epithelial cells in the ELS to increase their activity. H o w this labyrinthine t r a u m a - E L S reaction was mediated remains unknown. Clearly, the reaction began within 48 hours and continued for several days to weeks after the insult. Interestingly, the increase in ELS activity in response to perilymphatic injection of neomycin was prolonged when compared with ELS responses to specific labyrinthine insults, such as freezing the lateral ampulla. The ELS responses seen in this study reinforce the observations of others that aminoglycoside antibiotics have an ongoing destructive effect on cellular elements in the guinea pig cochlea and vestibular apparatus for periods of at leas[ several weeks, s,:~
GRAY ET AL.
The present study confirms the finding that the ELS increases its activity during periods of labyrinthine trauma and stress. Further, the present study suggests that, like some other cellular elements derived from the otocyst, most notably the strial epithelium and Reissner's membrane, the epithelium of the endolymphatic sac is not d e s t r o y e d by ototoxic levels of aminoglycoside antibiotics.
4.
5.
6. 7.
References 8. 1. Kohonen A: Effect of some ototoxic drugs upon the pattern and innervation of cochlear sensory cells in the guinea pig. Acta Otolaryngol suppl 208:1-70, 1965 2. Hunter-Duvar IM, Mount RJ: The organ of Corti following ototoxic antibiotic treatment, SEM/1978/II, pp 423 - 4 2 9 3. Leake-Jones PA, Vivion MC: Cochlear pathology in cats
9.
following administration of neomycin sulphate. SEM/ 1979/III, pp 983-991 Lundquist P-G: The endalymphatic duct and sac in the guinea pig. An electron microscopic and experimental investigation. Acta Otolaryngol suppl 201:1-108, 1965 Lundquist P-G, Kimura R, Wers~lll J: Ultrastructural organization of the epithelial lining in the endolymphatic duct and sac in the guinea pig. Acta Otolaryngol 57:65-80, 1965 Lundquist P-G: Aspects on endolymphatic sac morphology and function. Arch Oto-Rhino-Laryngal 212:231 240, 1976 Schindler RA, Lundquist P-G, Morrison MD: Endolymphatic sac response to cryosurgery of the lateral ampulla. Ann Otol Rhinol Laryngol 83:674--685, 1974 T e r a y a m a Y, Kaneko Y, Kawamoto K, et al: Ultrastructural changes of the nerve elements following disruption of the organ of Corti. Acta Otolaryngol 83:291-302, 1977 Kaneko Y, Terayama Y, Kawamoto K, et ah Single layer membrane covering the degenerated cochlear duct after perilymphatic perfusion of streptomycin. Acta Otolaryngol 86:375-384, 1978
Volume 3 Number 4 July 1982 2 (~1